Lapping plate



June 12, 1956 w. SODERMAN 2,749,683

LAPPING PLATE Filed Oct. 5, 1954 INVENTO/Q 6 W 6ODRMHN H T roan/5yUnited States Patent LAPPING PLATE George W. Soderman, Teaneck, N. J.,assignor to Western Electric Company, Incorporated, New York, N. Y., acorporation of New York This invention relates to abrading devices andparticularly to an improved surface lapping plate or disc.

One well known type of lapping plate used, for example, for grindingpiezo-electrical crystal wafers, consists of a flat metal plate havinggrid, or straight-line intersecting, grooved lapping surface.

It is customary to make such plates quite thick to allow for wear butthe intersecting grooves can be cut to only a limited initial depthwithout weakening the plate to the point where it tends to warp. As theplate wears, the grooves become too shallow for efficient operation but,due to the reduction in the mass of the plate, the grooves can bedeepened without causing it to warp. This groove deepening operation maybe repeated until the remaining metal becomes too thin to maintain aflat lapping surface. This procedure involves high maintenance expense,however, and when this type of lap is used thin quartz plates aresometimes chipped or broken by the sharp edges exposed at the ends ofthe grooves.

It is, therefore, the object of the present invention to overcome thedisadvantages of such lapping plates and to provide a strengthened orstiffer plate which will not require such periodic maintenance.

According to the invention, the face of a lapping plate has amultiplicity of non-intersecting annular grooves uniformly distributedover the lapping surface. Such grooves have no exposed sharp edges whichcan damage the work pieces.

Moreover, since they do not weaken the plate as do the intersecting gridgrooves, they may be cut initially to a depth giving a useful life equalto or greater than that obtainable by repeated regrooving of the oldtype plate.

These and other features of the invention will be more fully understoodfrom the following detailed description taken in conjunction with theaccompanying drawing, in which:

Fig. l is a plan view of the lapping surface of a plate according to thepresent invention;

Fig. 2 is a side elevational view partly in section of a pair of lappingplates of the type shown in Fig. 1.

In the drawing, an annular surface lapping plate 4 having an innercylindrical surface 5 and a concentric outer surface 6 is provided witha flat lapping surface 7. A plurality of non-intersecting annulargrooves 8 are cut into and are uniformly distributed over the surface 7.In a specific embodiment of the present invention designed for lappingquartz crystal Wafers, the plates 4 (and 11 as seen in Fig. 2) haveoutside diameters of inches, inner diameters of 3% inches and athickness d1 of 1 /2 inches. A total of 112 annular grooves or holes 8are provided in the lapping surface 7, the holes being substantiallyuniformly spaced in four concentric circles, 20 holes being in thesmallest circle and 24, 32 and 36 being in the second, third and fourthlarger circles. The annular grooves have an outer diameter of 7 of aninch, an inner diameter of of an inch and cut initially to a depth ofinch as contrasted with an initial cut of inch which is the maximumgroove depth feasible for a grid grooved plate of the prior art ofsimilar dimensions.

The inner and outer peripheral edges 9 and 10 respectively of thelapping surface are rounded to eliminate sharp edges which could breakwafers as the plates are moved in their circuitous lapping paths. In theprior art grid-grooved plates sharp edges cannot be entirely eliminatedfrom the peripheral edges 14 and 15 since the grooves 19 extend throughto these edges and some breakage of crystal wafers results when theplates are moved for the lapping operation.

As seen in Fig. 2 the top lapping plate 4 of a pair of lapping plates 4and 11 is provided with a concentric well 16 of depth d3 of about A ofan inch and a plurality of ports 17 for supplying abrasive paste to thelapping surfaces thereof. The crystal wafers being lapped are heldbetween the two plates 4 and 11 in apertures in a positioning plate 12located therebetween.

It is to be understood that the above described arrangements are simplyillustrative of the application of the principles of the invention.Numerous other arrangements may be readily devised by those skilled inthe art which will embody the principles of the invention and fallwithin the spirit and scope thereof.

What is claimed is:

l. A lapping plate having a fiat lapping surface with a plurality ofdeep non-intersecting annular grooves distributed uniformly thereover,the diameters of the grooves being small compared to the radius of theplate and said grooves being spaced apart to provide structuralrigidity.

2. A lapping plate comprising an annular metal disc having a flatlapping surface with a plurality of annular grooves distributeduniformly thereover, the diameters of the grooves being small comparedto the radius of the plate, said grooves being spaced apart to providestructural rigidity and the peripheral edges of the lapping surfacebeing rounded to prevent injury to articles being lapped thereby.

3. A lapping plate having a flat lapping surface with a plurality ofnon-intersecting annular grooves distributed uniformly thereover, all ofthe grooves being located entirely within the edges of the surface, thediameters of the grooves being small compared to the radius of the plateand said grooves being spaced apart to provide structural rigidity.

4. A lapping plate having a fiat lapping surface with a plurality ofnon-intersecting annular grooves distributed uniformly thereover, thegrooves being narrow with respect to the diameter thereof, the diametersof the grooves being small compared to the radius of the plate and saidgrooves being spaced apart to provide structural rigidity.

5. A circular lapping plate having a flat lapping surface with aplurality of non-intersecting annular grooves, spaced apart anddistributed uniformly thereover to provide structural rigidity, saidgrooves being spaced substantially uniformly about concentric circles inthe plate and the grooves being narrow with respect to the diameterthereof.

References Cited in the file of this patent UNITED STATES PATENTS1,405,424 Maynard Feb. 7, 1922 2,201,410 Simonds May 21, 1940 2,597,187Roshong May 20, 1952

